1. Field of Invention
The present invention relates to hydrocarbon well control in general and in particular methods and apparatuses for selectably opening and closing zones within a hydrocarbon well during completion, hydraulic fracturing or production.
2. Description of Related Art
In hydrocarbon production, it has become common to utilize directional or horizontal drilling to reach petroleum containing rocks, or formations, that are either at a horizontal distance from the drilling location. Horizontal drilling is also commonly utilized to extend the wellbore along a horizontal or inclined formation or to span across multiple formations with a single wellbore. With horizontal drilling the well casing is prone to resting upon the bottom of the wellbore requiring the use of spacers so as to centre the casing within the wellbore.
In horizontal hydrocarbon wells, it is frequently desirable to select which zone of the wellbore is to be opened for production or to stimulate one or more zones of the well to increase production of that zone from time to time. One current method of stimulating a portion of the well is through the use of hydraulic fracturing or fracing. One difficulty with conventional fracing systems, it that is necessary to isolate the zone to be stimulated on both the upper and lower ends thereof so as to limit the stimulation to the desired zone. Such isolation has typically been accomplished with sealing elements known as production packers located to either side of the zone to be isolated.
One of the prior problems with current fracing methods is that most hydrocarbon wells are constructed with a well casing located within the wellbore which is cemented in place by pumping cement down the casing to the bottom of the well so as to fill the annulus between the casing and the wellbore from the bottom up. Such concrete provides an additional barrier between the center of the well casing and wellbore which is to be fraced. In conventional methods, in order to thereafter frac a zone which has been constructed in such a manner, it is necessary to form a conduit from the interior of the casing to the wellbore wall by fracturing the cement as well as the formation. Needing to fracture the concrete as well as the formation increases the pressure required for the fracing process thereby increasing the equipment requirements as well as the resulting cost and time requirements.
Previous attempts to resolve some of the above difficulties has been to provide valves inline within the casing so as to selectably provide access to the desired zones of the well. Such valves may be sliding valves having actuators such as are described in US Patent Application Publication No. 2006/0207763 to Hofman published Sep. 21, 2006. With the use of such sliding valves however, it is still necessary to fracture, dissolve or otherwise perforate the concrete surrounding the casing to access the formation.